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Chemistry > Chapter 14 > Flashcards

Chapter 14 Flashcards

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1
Q

What is a redox reaction?

A

A reaction where electrons are transferred

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2
Q

What is a loss of electrons called?

A

An oxidation reaction

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3
Q

What is a gain of electrons called?

A

Reduction

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4
Q

When an element is oxidised, what happens to the value of its oxidation number?

A

It increases

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5
Q

What can electrochemical cells be made from?

A

Two different metals dipped in salt solutions of their own ions and connected by a wire

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6
Q

What do electrochemical cells do?

A

They create electricity

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7
Q

Why is it a redox process within an electrochemical cell?

A

Because there’s always two reaction with an electrochemical cell, one being an oxidation and one being a reduction reaction.

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8
Q

What is the anode in an electrochemical cell?

A

The anode is the negative electrode

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9
Q

What is the cathode in an electrochemical cell?

A

The cathode is the positive electrode

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10
Q

Does reduction occur at the anode or at the cathode?

A

Reduction occurs at the anode

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11
Q

Does oxidation occur at the anode or at the cathode?

A

Oxidation occurs at the cathode

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12
Q

Why does the reactive metal become the anode and the less reactive metal becomes the cathode in an electrochemical cell?

A

Because the reactive metal gives up its electrons and is oxidised and becomes the anode, where electrons flow from

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13
Q

In the electrochemical cell with zinc and copper, where zinc gives up its electrons more easily than copper, describe the half equations:

A

Zn –> Zn2+ + 2e-

Cu2+ +2e- –> Cu

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14
Q

In an electrochemical cell, where do electrons flow from?

A

Through the wire from the most reactive to the least reactive metal

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15
Q

In an electrochemical cell, how can you measure the voltage between the two half cells?

A

The voltage between the two half cells

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16
Q

What does the voltage between two half cells show?

A

The cell potential, and the direction of electron flow

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17
Q

In an electrochemical cell, what are the half cells connected by?

A

A salt bridge

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18
Q

What are slat bridges made from?

A

Filter paper soaked in a salt solution, e.g. KNO3

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19
Q

In an electrochemical cell where neither reactants or products are solids, why use platinum as an electrode?

A

It can conduct electricity and is inert

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20
Q

What is the problem with using platinum as an electrode?

A

It is very expensive, so graphite is often used instead

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21
Q

When drawing electrochemical cells, is the anode drawn on the right or left?

A

On the right

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22
Q

Are the reactions in an electrode reversible?

A

Yes

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23
Q

When setting up an electrochemical cell, how do we clean the surfaces of the metals?

A

We use a piece of emery paper or sand paper

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24
Q

How do we clean any oil or grease from the electrodes?

A

We use some propanone

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25
Q

Once the electrodes have been cleaned, describe how you set up an electrochemical cell:

A
  • Place each electrode into a beaker filled with a solution of ions of that metal
  • Create a salt bridge linking them together
  • Connect the electrodes to a voltmeter
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26
Q

What is an electrode potential?

A

A measure of how easy the substance in the half cell is oxidised

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27
Q

How does a potenital difference build up in the half cells?

A

As the substances in the half cells are oxidised or reduced, a potential difference is built up due to the difference in charge between the electrode and ions in solution

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28
Q

Does the half-equation with the more postive electrode potential go forwards or backwards?

A

Forwards

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29
Q

What are electrode potentials measured against?

A

Standard hydrogen potentials

30
Q

What is the definition of the standard electrode potential?

A

The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

31
Q

What are standard conditions?

A
  • Conc must me 1 mol/dm
  • 298K
  • 100kPa
32
Q

Is the standard hydrogen electrode shown on the left or on the right?

A

Always on the left

33
Q

What does the hydrogen half cell have a voltage reading of?

A

0V

34
Q

What is the equation for the reaction at the hydrogen electrode?

A

2H+ + 2e- –> H2

35
Q

How do you calculate the cell potential?

A

E reduction - E oxidation

36
Q

Why is the cell potential always a positive value?

A

The more negative E value is being subtracted from the more positive E value

37
Q

Why are standard conditions used when measuring electrode potentials?

A

Because the equilibrium condition is affected by changing conditions, so standard conditions are used

38
Q

In the conventional representation of electrochemical cells, which half cell goes on the left?

A

The half-cell with the more negative potential

39
Q

In the conventional representation of electrochemical cells, where does the oxidised for go?

A

In the centre of the diagram

40
Q

In the conventional representation of electrochemical cells, what do the double vertical lines represent?

A

The salt bridge

41
Q

In the conventional representation of electrochemical cells, what do the single vertical lines represent?

A

The different states

42
Q

In the conventional representation of electrochemical cells, what do commas represent?

A

Separate species that are in the same half-cell and in the same physical state

43
Q

In the conventional representation of electrochemical cells, if either of the half-cells uses platinum, lead or other inert electrodes, how are they shown?

A

On the outside of the diagram, separated by a single vertical line

44
Q

Wheat is the relationship between the size of the standard electrode potential and the reactivity of the metal?

A

The more reactive the metal, the more negative the value of the standard electrode potential

45
Q

What is the relationship between the size of the standard electrode potential and the reactivity of a non-metal?

A

The more reactive a non-metal is, the more positive the value of the standard electrode potential is

46
Q

How can you use electrode potentials to see if a reaction will happen or not?

A

If a reaction is thermodynamically feasible, the overall potential is positive

47
Q

The overall cell potential is -1.4V, will the reaction occur?

A

No the reaction is not thermodynamically feasible

48
Q

What happens during a disproportionation reaction?

A

An element is simultaneously oxidised and reduced

49
Q

Describe 2 situations where the prediction for whether a reaction is feasible or not may cause the prediction to be wrong?

A
  • When the conditions are not standard

- The reaction kinetics may not be favourable

50
Q

What is cell potential proportional to?

A

Total entropy change and lnk

51
Q

What are energy storage cells?

A

Batteries

52
Q

What can fuel cells generate energy from?

A

Hydrogen and oxygen

53
Q

What can hydrogen-oxygen fuel cells be used to power?

A

Electric vehicles

54
Q

In hydrogen-oxygen fuel cells, what is the electrolyte?

A

An aqueous alkaline KOH solution

55
Q

In hydrogne-oxygen fuel cells, what is fed into the anode and cathode?

A

The oxygen is fed into the positive cathode and the hydrogen is fed into the negative anode

56
Q

In hydrogen-oxygen fuel cells, how do the electrons flow?

A

From the negative anode through an external circuit to the positive cathode

57
Q

Where do the OH- ions pass through in a hydrogen-oxyegn fuel cell?

A

They pass through the anion-exchange membrane towards the negative electrode

58
Q

What is the overall effect of hydrogen oxygen fuel cells?

A

H2 and O2 react to form water

59
Q

At the anode, what does the platinum catalyst split the H2 into?

A

Protons and electrons

60
Q

What does the polymer electrolyte membrane do?

A

It only allows the H+ across and forces the e- to travel around the circuit to get to the cathode

61
Q

At the cathode, what does the O2 combine with?

A

The H+ from the anode and the e- from the circuit to form H2O

62
Q

In a manganate ion, what is the oxidation number of manganese?

A

7+

63
Q

What is a manganate ion?

A

Mn04 -

64
Q

When a manganate ion is reduced, what does the oxidation number of manganese go from to?

A

+7 to 2+

65
Q

What is a dichromate ion?

A

Cr207 2-

66
Q

What is the oxidation number of chronium in dichromate?

A

+6

67
Q

When dichromate is reduced, what does the oxidation number of chronium go from to?

A

+6 to +3

68
Q

When performing a redox titration, why is excess dilute sulfuric acid added to the flask?

A

So that there are plenty of H+ ions to allow the oxidising agent to be reduced

69
Q

When performing a redox titration with mangante ions, describe when you can tell when you reach the end point:

A

It is tainted with the purple colour of MnO4 -

70
Q

What is an iodate ion?

A

I03 -

71
Q

What does I03 - + 5I- + 6H+ react to form?

A

3I2 + 3H20

72
Q

What do you react iodine with to calculate the number of moles of iodine produced?

A

Sodium thiosulfate: I2 + 2S2O3 2- –> 2I- + S4O6 2-

You add sodium thiosulfate one drop at a time until the blue colour dissapears, which indicates all the iodine has reacted

Chemistry (25 decks)

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